Teaching of tricarboxylic acid cycle via decarboxylation clues

Abstract:

The tricarboxylic acid (TCA) cycle is a crucial yet challenging topic in the teaching of Biochemistry due to its complex reactions and dense knowledge points. Conventional teaching method typically follows the sequence of the reactions in the TCA cycle, which often resulting in suboptimal learning outcomes. This paper introduces an alternative teaching method with introduction of decarboxylation clues to simplify the reaction process and product terminology in the TCA cycle, making it easier for students to understand the pathways and mechanisms involved. Firstly, the dissection of decarboxylation demonstrates that pyruvate undergoes decarboxylation to form acetyl-CoA, which reacts with oxaloacetate to produce the 2-carboxymethyl group in citrate. This 2-carboxymethyl group does not participate in decarboxylation during the first round of the TCA cycle. Subsequently, with R representing carboxymethyl for analyzing the TCA cycle, it is found that starting from the condensation of acetyl-CoA and oxaloacetate, the chemical formulas of some intermediates in the TCA cycle can be correspondingly written as follows: citrate (R-2-malate), cis-aconitate (R-fumarate), isocitrate (R-3-malate), α-ketoglutarate (R-pyruvate), succinyl-CoA (R-acetyl-CoA), and succinate (R-acetate). The two decarboxylation steps in the TCA cycle occur in isocitrate and α-ketoglutarate, respectively. To evaluate the effectiveness of this new teaching method, we recruited students to participate in a survey assessing their learning outcomes before and after teaching with this method. Statistical analysis of the feedback results showed that the majority of students taught with this new method found each step of the TCA cycle easier to understand and remember, with significant improvement in learning outcomes. The teaching method with decarboxylation clues enhances learning outcomes by stimulating students’ thinking and analysis and promoting their learning initiative and innovative spirit, thereby leading to better learning results.